Uranus – Planet Profile

Uranus was unknown before 1781 when William Herschel discovered it using a telescope. It was therefore the first planet to be discovered by modern astronomy.

Prior to this and going back to ancient times, only the five planets which can be seen with the unaided eye (Mercury, Venus, Mars, Jupiter and Saturn) were known.

Uranus is another “Gas Giant” and much larger than Earth, although it is smaller than Jupiter and Saturn. Uranus is about 31,000 miles in diameter at the equator, but less at the poles due to rotational flattening.

Uranus orbits around the Sun, once every 84 Earth years.

It rotates about its axis, once every 17 hours.

The axis of Uranus is uniquely (for a planet in the Solar System) tilted over at the extreme angle of 82 degrees to its orbital plane. This means that from Earth, we sometimes see a polar region and other times an equatorial region.

On Uranus, the axial tilt means that each polar area is dark for 42 Earth years, and then light for 42 Earth years!

We do not know why the axis of Uranus is tilted so much. Some people think it was the result of a huge collision, long ago.

Observing Uranus from Earth reveals no detail on the planet’s disk, even with a large telescope. It does however look blue-green in colour, due to frozen methane in the atmosphere.

Uranus’ five largest satellite moons can be seen from Earth. These are called Miranda, Ariel, Umbriel, Titania and Oberon. All are smaller than our Moon. Titania is the largest.

A remarkable discovery was made in 1977, from Earth. During observation of Uranus occulting (passing in front of) a star, faint rings around the planet were suspected but not confirmed.

Then came the Voyager space probe of 1986 and the rings were clearly seen by it, as it flew past. There are 11 rings in total and they are very thin, probably less than one mile thick.

Voyager also took some remarkable images of Uranus’ satellite moons, especially Miranda which has a strange varied surface.

Uranus has a total of 21 known satellite moons.

Podcast: Play in new window | Download